Despite the rise of bacterial resistance to antibiotics, the development of new antibiotics is on the decline. Methicillin-resistant Staphococcal aureus infections (MRSA) in the United States has been increasing, causing 19,000 deaths per year in the United States and contributing to $3 billion to $4 billion of additional annual health care costs. The issue of combating resistance has been exacerbated by the relative scarcity of new chemical scaffolds discovered or developed. Most of the antibacterial research at pharmaceutical companies has been towards developing analogs of existing drugs through traditional chemistry driven SAR programs. Very few new classes of antibiotics have been introduced in the past decades, and most antibiotics act on familiar targets. In addition, even though natural products have been a rich source of new antibacterials, many pharmaceutical companies have natural product libraries that have been thoroughly screened and offer little in the way of diversity or novelty. There is a growing awareness that natural product libraries, particularly those with a fungal origin, need to exploit fungal cryptic or secret pathways that normally are not expressed in laboratory conditions. To exploit the largely undiscovered secondary metabolites of mushrooms (basidiomycetes and ascomycetes), LifePharms, Inc. has established a collection of field- collected, environmentally challenged fruiting bodies. LifePharms/Microbiotix collaboration has identified, purified, and characterized two compounds that exhibit potent antibacterial activity (MICs as low as 0.5 5g/ml) against Gram-positive pathogens, including MSSA, MRSA, MRSE, and VRE, and favorable cytotoxicity profiles (CC50 > 100 5g/ml). The chemical structures of these two lead compounds indicate they are novel antibacterial compounds. In addition, we have purified and partially characterized three more potent antibacterial compounds that will serve as alternative scaffolds. In this Phase I grant, we will i) evaluate these compounds in a series of in vitro assays that will measure ADMET, ii) chemically optimize these compounds by generating analogs using semi-synthetic methodologies to determine structure activity relationships and to improve potency and selectivity, iii) Data obtained from these assays will inform the design of subsequent analogs, resulting in an iterative process of analog design and evaluation, to improve the efficacy, selectivity, and ADMET properties of the scaffolds. In Phase II, compounds that meet the specified criteria for efficacy, selectivity, and ADMET properties will be tested for acute toxicity and antibacterial efficacy in mice.